I've been researching this too.
I've been waffling between getting a diesel engine (in the hope of eventually switching over to biodiesel), or to go with an electric inboard, such as the Thoosa 7000 (suitable for my 27' ft sloop).
Since I only am a daysailer/weekender, and usually only cruise less than 50 miles from port, I would feel comfortable with the range afforded by the inboard electric, especially seeing as those nifty Thoosa's can regenerate the batteries when the engine is off by using the slowly turning prop as a dynamo for power generation (this power generation can even work using a feathering prop, but obviously less effectively). Coupled with a solar panel or two, maybe a wind genset, my batteries could basically maintain themselves during the week when I'm not using the boat, which would eliminate the need for a shorepower connection to top up the batteries (my boat is on a mooring, so shorepower is out).
Like I said, I'm basically a weekender, so I dont need to motor for hundreds of miles. I motor in and out of the harbor, or over to the pump-out dock, thats it. If I'm trying to evade a storm, sometimes I'll fire up the motor, however, and that might take more juice than the batteries could provide. If I needed more range with the Thoosa, I could install a diesel generator to top up the batteries, or, if I'm feeling like a cheapskate, I could just use my Honda 2000i gas genny to give me enough juice to maintain the batteries for longer trips under power.
Anyway, since the Thoosa package sells for just over $7k
, I'll have plenty of time to debate between biodiesel and electric as I save my pennies for the next few years.
Hopefully, by the time I've made my decision, the cost of batteries and electric marine inboards willhave come down a bit.